Abstract

Salicylic acid and major metabolite concentrations were determined in catheterized channel catfish following IV and PO administration of sodium salicylate (44 mg/kg). Following administration, blood samples were taken for 72 hours and were analyzed for salicylic acid by HPLC. The following pharmacokinetic parameters were calculated: t1/2(a) = 0.31 hr, t1/2(b) = 7.02 hr, Vd(area) = 227.4 ml/kg, Vd(ss) = 196.3 ml/kg, CIB = 17.2 ml/kg/min, t1/2(abs) = 0.47 hr, T(lag) = 0.022 hr, and F = 0.84. Urine and bowel contents were analyzed for the presence of salicylic acid and major metabolites, gentisic acid, gentisuric acid and 2,3-dihydroxybenzoic acid, for 48 hr following oral drug administration. Salicylic acid and gentisic acid were detected in urine for 24 hr following administration, while salicylic acid could be detected in bowel contents for up to 24 hr.

Introduction

Aspirin is a widely used antipyretic and analgesic for the treatment of pain and inflammatory disorders in humans and several species of animals. Following oral administration, the parent compound is rapidly hydrolyzed to salicylic acid. When administered IV or PO, sodium salicylate, a closely related compound, is converted to salicylic acid in the blood or absorptive membrane. Salicylic acid is cleared partly by renal clearance of parent compound or by hepatic transformation along several metabolic pathways. Possible metabolites are gentisic acid, gentisuric acid, 2,3-dihydroxybenzoic acid, salicyluric acid, and salicyl phenolic glucuronide, among others.

Sodium salicylate has served as a model drug for multiple pathway elimination, and was chosen to determine metabolic and elimination pathways in the channel catfish. Also sodium salicylate was used to determine what combinations and concentrations of parent compound and metabolites were eliminated in catfish urine and feces following oral administration. The purpose of the current study was to estimate the pharmacokinetics of sodium salicylate following IV and PO administration, and to quantitate parent compound and metabolites in urine and feces.

Materials and Methods

Adult channel catfish of either sex, weighing approximately 1 kg each were used. The fish were acclimated for at least 14 days prior to use in the study. Water temperature was maintained at 22C and oxygen concentration was regulated at 7 ppm throughout the experimental period.

The catfish were catheterized for chronic blood sampling by a technique developed in our laboratory.¹ Briefly, the catfish were anesthetized in an 80L aquarium using 3-aminobenzoic acid ethyl ester (MS-222) at a concentration of 1:10,000. When anesthetized, a catheter was placed in the dorsal aorta using a cather-inside-needle arrangement. After removing the needle, the catheter was sutured in place. The fish were placed in custom designed plexiglas chambers supplied with temperature and oxygen controlled water in a flow-through design. The blood collection catheter was passed through a rubber stopper to the outside of the chamber for sampling with minimal stress to the fish.

Sodium salicylate was administered IV or PO (44 mg/kg) to the catheterized catfish. One ml blood samples were taken in heparinized collection tubes at 0, 0.08, 0.17, 0.5, 1, 2, 4, 8, 12, 18, 24, 30, 36, 48, 54, 60, and 72 hrs after administration. Equivalent volumes of saline were injected to replace the blood taken at sampling periods. The plasma was separated by centrifugation (1100 xg) and stored at -70C until analyzed. In addition, urine and bowel contents were collected at 0, 4, 8, 12, 24, and 48 hrs after PO administration and were assayed for parent compound and metabolites of sodium salicylate. The blood, urine, and bowel content samples were analyzed for concentrations of salicylate and metabolites by high performance liquid chromatography (HPLC).

Pharmacokinetic calculations were based on a 2-compartment open model for the IV study, and first-order absorption following oral administration. A regression technique weighted by the factor J/Y2 was used to determine alpha and beta values for the curve of best fit. Individual values of A, B, alpha, and beta were calculated, meaned, and reported as mean +/- SID. Other pharmacokinetic parameters including VD(area), Vd(ss), CIB, MRT, t1/2(abs), and t(lag) were determined using standard calculations.²

Results

Pharmacokinetic values estimated for the IV and PO studies are presented in Table 1. A 2-compartment open model was used to best describe the resulting plasma concentration versus time values. Pharmacokinetic values are reported as mean ± SID where appropriate.

Table 1. Pharmacokinetic values for IV and PO administration of sodium salicylate (44 mg/kg)

The parent compound, salicylic acid, was detected in catfish urine and in bowel contents at 4, 8, 12, and 24 hrs following oral administration, but could not be detected at 48 hrs. Only one metabolite, gentisic acid, was detected in fish urine at 8, 12, and 24 hrs following dosing. No metabolite of salicylic acid was detected in bowel contents at any time point. Parent compound and metabolite concentrations are presented in Table 2.

Table 2. Mean concentration (± SD) (μg/g) of salicylic acid and its metabolite in catfish urine and bowel content. N = 5.

Discussion

The pharmacokinetic parameters for salicylate in the channel catfish differ from other domestic species and humans. The biological half-life of 7 hrs in the fish was intermediate between the dog (3-9 hr)(3-5) and cat (11.0 hr)(3), equivalent to the horse (7 hr)(6), longer than the buffalo (2 hr)(7), and humans (2.1-3.1 hr)(8). The volume of distribution of salicylate in catfish (0.196 - 0.227 L/kg) was small, indicating poor tissue penetration due to low lipid solubility and rapid elimination by the kidneys. The bioavailability indicated that sodium salicylate was well absorbed following oral administration, and that the drug could probably be successfully administered in feed or water to the fish.

The catfish in this study eliminated salicylate primarily unchanged in urine and bowel contents. Even though the drug was well absorbed following oral administration, approximately 10 times more drug was eliminated in bowel contents than in urine at each time point. This could be explained by active secretion into the GI tract or by enterohepatic recycling of the drug.

A single metabolite, gentisic acid, was eliminated in very low concentrations in the catfish urine. This is in agreement with other species.^2,4 It is reasonable to speculate that salicylate experiences similar absorption, distribution, metabolism, and excretion in the channel catfish compared to other animal species. Further study of this drug in catfish is needed to explain the large GI tract excretion of parent compound compared to renal excretion.

References

1.  Kitzman JV, Holley JH, Huber WG. 1988. Sample collection techniques in the channel catfish during prolonged pharmacokinetic experiments. Vet Human Tox 30:12-13.

2.  Gibaldi M and Perrier D. 1982. Eds. Pharmacokinetics, Marcel Dekker Inc., NY.

3.  Akesson CE, Linero PEM. 1982. Effect of chloramphenicol on serum salicylate concentrations in cats and dogs. Am J Vet Res 43(8):1471 1472.

4.  Davis LE and Westfall BA. 1972. Species differences in biotransformation and excretion of salicylate. Am J Vet Res 33.1253-1262.

5.  Abbit LE, Davis LE, Neff-Davis CA. 1978. Effect of toxic hepatitis on pharmacokinetics of salicylate in dogs. J Vet Pharmacol Therap 1:299-308.

6.  Beaumier PM, Fenwick JD, Stevenson AJ, et al. 1987. Presence of salicylic acid in standardbred horse urine and plasma after various feed and drug administrations. Equine Vet J 19(3):207-213.

7.  Narasimhaiah N, Narayana K, and Gowda DKV. 1984. The effect of ammonium chloride on -the blood plasma concentration and pharmacokinetics of sodium salicylate in the buffalo calf. Indian Vet J 61 (8):654-658.

8.  Greenblatt DJ, Abernethy DR, Boxenbaum HG, et al. 1986. Influence of age, gender, and obesity on salicylate kinetics following single doses of aspirin. Arthr Rheum 29(8):971-980.